3-D Analytical Model and Direct Measurement Method of Ultra-Thin Open-Circuit Air-Gap Field of Interior Permanent Magnet Synchronous Motor with Multi-Segmented Skew Poles and Multi-Layered Flat Wire Windings for Electric Vehicle

3-D analytical model and direct measurement method (DMM) of ultra-thin open-circuit air-gap field (OCAGF) of interior permanent magnet synchronous motor (IPMSM) with multi-segmented skew poles (MSP) and multi-layered flat wire windings (MFWW) for electric vehicles (EV) are proposed. Basis functions of slotless OCAGF are derived through field reconstruction method (FRM). In order to consider MSP and slotting effects, a complex relative permeance function is extended from 2-D to 3-D. Based on the magnetic potential and permeance method, 3-D analytical model of OCAGF is obtained. Then the back electromotive force (BEF) is calculated through Faraday's Law and the cogging torque is obtained through Maxwell stress tensor method. Furthermore, spatial order and amplitude-frequency characteristics of OCAGF are revealed. Additionally, influence of local inhomogeneous saturation caused by PM materials on analytical accuracy is discussed. Finally, the proposed analytical model is verified through both the traditional indirect measurement methods (BEF measurement and cogging torque measurement) and a novel direct measurement method, in which ultra-thin OCAGF of 10-1 mm order of magnitude can be measured directly. Local microscopic characteristics of OCAGF in some important locations, such as tooth top and magnetic bridge, can be accurately detected by using of the direct measurement method.